For the servicing of small vehicles such as snowmobiles, all terrain vehicles, small tractors, motorcycles, and the like, dedicated load lifting devices have been developed in the past. These vehicle servicing lifts usually include a platform, onto which rests the vehicle, and a power lift means--usually hydraulic--for vertically displacing the platform over ground. The vehicle raised by the power means onto its platform defines therebeneath a ground clearance, about which a mechanic can freely stand to work on the vehicle.
U.S. Pat. No. 3,788,414 issued in 1974 to Netter is typical of such lifts. The power means is a hydraulic ram, referenced 30, coupled to a hydraulic fluid source via hydraulic line 40. Of course, this hydraulic line renders the lift dependent upon a building installation having a hydraulic fluid supply to feed the hydraulic line 40. Accordingly, such lifts are not self-contained, i.e. that they rely on an external supply of fluid to operate. Another disadvantage of this patent is that, should the hydraulic pressure accidentally fall in the extended ram, a dangerous condition would occur in that the vehicle supporting platform would fall immediately onto the mechanic working thereunder.
Canadian patent 263,648 issued in 1926 to Walker Manufacturing Co., discloses a lifting jack having a deformable parallelogram linkage 8, 10 which introduces a measure of built-in safety feature into the lift to dampen the reaction of the lift should the hydraulic pressure fail.
Similar parallelogram linkage assemblies are found in the following lift jack patents: U.S. Pat. Nos. 3,788,414; 2,747,652; as well as 4,979,723.
All these prior art patents require an external power source i.e. a hydraulic fluid supply or a pressurized air supply. They are therefore dependent upon such an external power source, and thus, cannot be self-enclosed, portable units.